Abstract:

A method and system for printing image documents using a variety of
toners where some toners using a multi-development station having two or
more development stations. These toners are co-printed prior to fixing,
on the receiver by the multi-development station.

Claims:

1. A method of maintaining print quality during printing using an
electrophotographic print engine comprising: a. checking for any resource
errors that indicate unavailable resources to enable processing the image
data as directed by a job specification; b. indicating errors with an
indicator before creating an electrostatic latent image corresponding to
the separation by image-wise exposing the primary imaging member; c.
converting the electrostatic latent image into a visible image using a
the multi development station; d. transferring the image to a receiver;
and e. permanently fixing the image to the receiver.

2. The method according to claim 1 whereby the indicator specifies the
development station to deposit the specialty toner.

3. The method according to claim 1 whereby an operator receives the
indicator.

4. The method according to claim 1 whereby the toner is a specialty item.

5. The method according to claim 1 whereby the print engine selects the
development station to deposit the toner based on job information.

6. The method according to claim 1 whereby one or more development
stations of the multi-development station contains a marking that informs
the electrophotographic print engine as to the contents of the one or
more development station.

7. The method according to claim 1 whereby the operator inputs a new
resource for the electrophotographic print engine based on the indicator.

8. The method according to claim 1 whereby the job specification creates
a conflict, said job conflict creates an error message and pauses the
print job pending resolution of the conflict.

9. The method according to claim 8 using a diverter that allows either
duplex or multipass simplex printing as a resolution of the conflict.

10. The method according to claim 8 whereby said conflict is resolved by
overprinting a simplex image.

11. The method according to claim 8 whereby the conflict is resolved
using a look up table (LUT).

12. An electrophotographic printer engine comprising; a. a single
development station; b. at least one multi-development station; c. two or
more primary imaging members; and d. a control unit such that said
control unit: e. checking for any resource errors that indicate
unavailable resources to enable processing the image data as directed; f.
indicating errors with an indicator before creating an electrostatic
latent image corresponding to the separation by image-wise exposing the
primary imaging member; and g. converting the electrostatic latent image
into a visible image using a the multi development station.

13. The method according to claim 12 whereby the indicator specifies the
development station to deposit the specialty toner.

14. The method according to claim 12 whereby an operator receives the
indicator.

15. The method according to claim 12 whereby the toner is a specialty
item.

16. The method according to claim 12 whereby the print engine selects the
development station to deposit the toner based on job information.

17. The method according to claim 12 whereby one or more development
stations of the multi-development station contains a marking that informs
the electrophotographic print engine as to the contents of the one or
more development station.

18. The method according to claim 12 whereby the operator inputs a new
resource for the electrophotographic print engine based on the indicator.

19. The method according to claim 12 whereby the job specification
creates a conflict, said job conflict creates an error message and pauses
the print job pending resolution of the conflict.

20. The method according to claim 19 using a diverter that allows either
duplex or multipass simplex printing as a resolution of the conflict.

21. The method according to claim 19 whereby said conflict is resolved by
overprinting a simplex image.

22. The method according to claim 19 whereby the conflict is resolved
using a look up table (LUT).

[0002] This invention relates to an electrophotographic print engine. More
specifically, this invention describes an apparatus capable of printing
images using a multi development station.

BACKGROUND OF THE INVENTION

[0003] In order to produce a print using electrophotographic means, a
primary imaging member, also referred to as a photoreceptor or a
photoconductor, is first uniformly charged. An electrostatic latent image
is then formed by image-wise exposing the charged using known methods
such as an optical exposure system, an LED array, or a laser scanner. The
primary imaging member is then brought into close proximity to a
development station that contains electrically charged marking particles,
often referred to as toner or dry ink so that the marking particles
selectively adhere to the electrostatic latent image, thereby converting
it into a visible image. The image is then transferred to an intermediate
transfer member or directly to a receiver. The visible image on the
receiver is then made permanent by fixing or fusing the image by, for
example, subjecting the image-bearing receiver to a combination of heat
and pressure. If desired, a gloss can be imparted onto the image by
casting the image against a ferrotyping member, as is known in the art.
The primary imaging member is then cleaned and made ready to produce a
subsequent print.

[0004] To produce a color image, electrostatic latent images are formed
corresponding to the subtractive primary colorant information, i.e. the
cyan, magenta, yellow, and black colors of that comprise the color gamut
of the image to be printed. These images, frequently referred to as
separations, are transferred in register either to a receiver directly or
to an intermediate member and then to the receiver. The image is then
fixed, as described above.

[0005] Two distinct electrophotographic engine designs are used to produce
color images using an electrophotographic module to produce an
electrophotographic image. The first is an electrophotographic module
that contains a primary imaging member, a primary charger, a means for
creating an electrostatic latent image, a means for converting the
electrostatic latent image into a visible image, and a means for
transferring the visible image to either a transfer intermediate member
or a receiver. The electrophotographic module can also contain
appropriate cleaning devices or means to remove residual toner, etc.
where necessary and appropriate. The printer also has other components
not in the electrophotographic modules, such as a fuser, a receiver or
paper feeding device, finishing devices such as staplers, stackers,
collators, etc. In some printers there are also intermodule components
such as a paper inverter.

[0006] In some instances components can be shared by more than one module.
For example, a single primary imaging member in the form of a web can be
used to create the electrostatic latent image corresponding to each of
the separations. In this example, it is generally preferred to have
different frames of the web primary imaging member used for each
separation and then transfer the separations sequentially and in register
to either an intermediate member or to a receiver. It is generally not
desirable to use a cylindrical primary imaging member as a shared
component in multiple electrophotographic modules as the size of such a
cylinder would be prohibitively large and expensive.

[0007] Currently any electrophotographic engines with a plurality of
development stations located in proximity to a single primary imaging
member produce color prints by serially developing electrostatic latent
images onto a primary imaging member. These engines require that a toned
image be first transferred from the primary imaging member prior to the
formation of a subsequent electrostatic latent image and the conversion
of the electrostatic latent image into a visible image or the polarity of
the charge of the toner in the two stations be opposite. In either
application, converting the electrostatic latent image to a multiple of
images with differing colors or toners requires that the sequential
charging, formation of the electrostatic latent image, and conversion of
the electrostatic latent image into a visible image. Thus, an image
requiring two colors takes at least twice as long as that described in
the present invention. For example an image requiring four colors would
take four times as long to produce as one utilizing a single color.

[0008] Also present electrophotographic printers have other limitations.
The color gamut obtainable is limited to that area in color space spanned
by the subtractive primary colored toners. Thus, colors that contain
vivid reds or greens might not be printable. Green, red, orange, blue,
and violet toners are specialty toners that are used to enhance the
available color gamut. Custom spot colors such as are commonly used in
corporate logos are often outside the realm of the color gamut obtainable
with standard subtractive primary colors. Magnetic recording inks, called
MICR toners, are often used by banks to mark checks. These generally
require a separate development station. The density versus the log of the
exposure, often referred to as the D-log E curve, tends to become flat in
both the low and high density regions of a print. These regions are
referred to as the toe and shoulder, respectively, and are accompanied by
a loss of information. It simply is not possible to differentially
deposit varying amounts of toner in these regions to enhance the
information. However, amounts of toner having a lower than normal
colorant density or extinction coefficient can enhance the information
content of these regions.

[0009] Another example of the limitation of the present technology is that
there are many types of specialty toner required for one print. For
example, normal-size clear toner particles, i.e. those having median
volume weighted diameters in the range of approximately 5 μm to 8
μm, are often used to cover exposed portions of a receiver such as
paper to enable an image on that receiver to be uniformly glossed and
large clear toner, i.e. that having a median volume-weighted diameter of
greater than approximately 20 μm, is often used to produce raised
letter printing. In addition, toner particles are often used that contain
security features that might be desired in the print, such as toner
particles can contain so-called traceless components that would allow
only certain detectors to detect the presence of the component. Combining
all these toners, called specialty toners, into one latent images is not
currently possible in one pass since in most electrophotographic print
engines, the receiver is in sheet format. Transporting a sheet through a
large number of electrophotographic modules is problematic and can lead
to misregistration as well as artifacts such as fuser oil being
transported back to a sheet from a transport web. As the length of the
web increases to allow for additional electrophotographic modules, the
probability of back transferring fuser oil from the transport web to the
receiver increases.

[0010] In addition, these toner particles are often highly charged
electrically. If there are too many toner particles present, such often
occurs when multiple layers of toner are present, the electrostatic field
used to transfer the toner is screened by the toner charge, thereby
reducing the transfer field and impeding transfer. Thus, it is often
difficult to transfer an arbitrarily large number of toner layers, in
contrast to the lithographic printing of an arbitrarily large number of
offset printed separations.

[0011] Finally, the space available for electrophotographic print engines
is generally much more restricted than that available for offset presses.

[0012] The present invention allows all the printing of these specialty
toners into one printer using one or more multi-development status.

SUMMARY OF THE INVENTION

[0013] This invention relates to an electrophotographic print engine
having multi development stations that can print a variety of toners
including certain specialty toners using a relatively compact engine. The
specialty toners can be designed to enhance color gamut, apply specialty
toners such as magnetic toners used by banks for tracking checks, a.k.a.
MICR (toner used to print magnetic characters), clear toners use for
purposes such as enhancing gloss, providing abrasion resistance, etc.,
toners containing security features such as so-called "traceless
components", etc. The printing of at least some of the electrostatic
latent images formed on a primary imaging member into visible images uses
one or more multi-development stations to convert an electrostatic latent
image on a primary imaging member or a frame of a primary imaging member
into a visible image. The image is ultimately transferred to a receiver
in register with other images that had been or will be transferred to the
receiver. The station can be chosen either by the operator or by a
process control or feedback mechanism that would call for that particular
toner. The final print would thus be able to have multiple toners because
the multi development station would contain a plurality of development
stations would be able to deposit multiple toners onto the eventually
formed print. This invention allows an electrophotographic print engine
to print using many specialty inks without unduly increasing its size.

[0014] As a result of these constraints, it is readily apparent that an
arbitrarily large number of electrophotographic modules cannot be
incorporated into a typical electrophotographic engine, despite the need
to enable printing using specialty toners to augment the capabilities of
the substractive primaries. It is the goal of this invention to describe
a method and apparatus capable of meeting this requirement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIGS. 1a and 1b depict two embodiments of the present invention.

[0016] FIG. 2 depicts another embodiment of the present invention.

[0017]FIG. 3 shows a diverter that is positioned so as to allow a
receiver sheet to be reprinted in the simplex mode according to the
present invention.

[0018]FIG. 4 shows a diverter that is positioned so as to allow a
receiver sheet to be reprinted in the duplex mode according to the
present invention.

[0019]FIG. 5 shows an electrophotographic print apparatus containing two
diverters according to the present invention.

[0020]FIG. 6 shows a configuration with a multipass simplex paper path
according to the present invention.

[0021]FIG. 7 shows a method of using skew and position sensors for
tracking the position of a receiver sheet in a multipass simplex
operation of the present invention.

[0023]FIG. 9 shows an embodiment of a method of correcting errors
according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] FIG. 1 shows a electrophotographic (EP) engine (100) or printer,
often referred to as a tandem print engine including EP modules (110A,
110B, 110C, 110D, and 110E), wherein each contains a single primary
imaging member (115A, 115B, 115C, 115D, and 115E) and a single
development station (117A, 117B, 117C, 117D, and 117E) to print on
receiver 111. In addition, a sixth EP module (112) is shown containing
development stations 113A and 113B which form a multi-development station
114. The EP printer is shown having dimensions of A×B which are
around in one example, 52×718 mm or less. FIG. 2 shows a slightly
larger printer where B is expanded to accommodate the second
multi-development engine. This new engine is designed so that the
multi-development stations are able to be incorporated into a smaller
engine using larger imaging members than are normally used. Development
stations 110A though 110E would typically contain toner (T) that is
typically used in most color prints. For example, toner having typical
optical densities such that a monolayer coverage (i.e. sufficient toner
such that a microscopic examination would reveal a layer of toner
covering between 60% and 100% of a primary imaging member would have a
transmission density in the primarily absorbed light color, as measured
using a device such as an X-Rite Densitometer with Status A filters of
between 0.6 and 1.0) of the subtractive primary colors cyan, magenta,
yellow, and black would typically be contained in four of these
development stations. The multi development station can be used to print
for a toner that is commonly used for many applications, selectively
determined by a control element. An individual operating or owning
(hereafter referred to as the operator) the EP engine could control the
control element and this effectively determines which specialty toner
would print.

[0025] For example, a full-color image can be made using toner or ink
containing typical cyan, magenta, yellow, and black subtractive primary
colorants such as pigment particles or dyes. Each toner is contained in a
development station that develops an electrostatic latent image and is in
proximity to a cylindrical primary imaging member or a frame of a primary
imaging member in the form of a continuous web. Additional toners
corresponding to specialty toners or inks are contained in one of a
plurality of development stations, any one of which can be brought into
proximity with a primary imaging member bearing an electrostatic latent
image and convert that electrostatic latent image into a visible image.
For example, an electrophotographic engine can contain five print
modules. Four of the modules would each contain a single development
station containing toners of one of the four subtractive primary colors.
The fifth module is shown with a multi-development station, having a
plurality of development stations, each containing a distinct specialty
ink that can convert an electrostatic latent image into a visible image
with only that specific specialty ink.

[0026] For example, if clear toner is commonly used by a particular EP
engine, the fifth station could contain clear toner. Alternatively, other
toners that would be commonly used throughout a variety of jobs can be
contained in the fifth station. Development stations suitable for use in
this invention include dry development stations containing two component
developers such as those containing both toner particles and magnetic
carrier particles, or single component development stations. The
development stations used for two component development can have either a
rotating magnetic core, a rotating shell around a fixed magnetic core, or
a rotating magnetic core and a rotating magnetic shell. Single component
development stations suitable for use in this invention are known in the
literature. It is preferred that the toners used in practicing this
invention are a component of dry developers.

[0027] The sixth EP module 112 with the multi-development station 114 is
capable of selectively printing one or more toners such as K-K (black and
black), two colors including black and/or a color and a specialty toner.
Specialty toners include transparent, raised print, MICR magnetic
characters, specialty colors and metallic toners as well as other
specialty toners that are not the basic color toners. The
multi-development station 114 can have two (as shown in FIG. 1a) or more
development stations in communication to one photo conductor so that the
two or more development stations deposit toner onto an electrostatic
latent image on primary imaging member 115F. In another embodiment, as
shown in FIG. 1b the multi-development station is a monocomponent module
which can be integrated with dual component or monocomponent development
stations giving even more stability. Here one or both stations can
deposit toner onto the primary imaging member during a single pass of a
receiver through the EP engine. The larger photo conductor enables the
location of the multi development station 114 shown.

[0028] In the example shown in FIG. 1a, after each development station
develops the electrostatic latent image on the primary imaging member
(PIM), thereby converting the electrostatic latent image a visible image,
each image is transferred, in register, to an intermediate transfer
member (ITM) 150. The ITM can be in the form of a continuous web as shown
or can take other forms such as a drum or sheet. It is preferable to use
a compliant intermediate transfer member, such as described in the
literature, but noncompliant ITMs can also be used.

[0029] The receiver sheets 111 are held in the printer at the paper tray
105 and, in the example shown, enter the paper path 180 so as to travel
initially in a clockwise direction. The paper could also be manually
input. The printed image is transferred from the ITM to the receiver and
the image bearing receiver then passes through a fuser 170 where the
image is permanently fixed to the receiver. The image then enters a
region where the receiver either enters an inverter 185, continuing to
travel clockwise, stops, and then travels counterclockwise back onto the
paper path 180. This inverts the image, thereby allowing the image to be
duplexed. Prior to the inverter is a diverter 152 that diverts the
receiver sheet from the inverter and sends it back along the paper path
in a counterclockwise direction. This allows multiple passes of the
receiver on the simplex side, as might be desired if multiple specialty
toners contained in the multi development station 114, shown here as
development stations 113A and 113B, are to be used in a printer or if
special effects such as raised letter printing using large clear toner is
to be used. It should be noted that, if desired, the fuser 170 can be
disabled so as to allow a simplex image to pass through the fuser without
fusing, if desired. This might be the case if an expanded color balance
in simple printing is desired and a first fusing step might compromise
color blending during the second pass through the EP engine. Operation of
the diverter to enable a repeat of simplex and duplex printing is shown
in FIGS. 3 and 4, respectively. Alternatively, a fusing system that
merely tacks, rather than fully fuses, an image and is known in the
literature can be used if desired such as when multiple simplex images
are to be produced. The image can also be sent through a subsystem that
imparts a high gloss to the image, as is known in the literature and is
described in co-owned U.S. Pat. Nos. 7,212,772; 7,324,240 and 7,468,820
as well as U.S. Publications 2008/159786 and 2008/0050667, which are
hereby incorporated by reference. This is especially important as one
embodiment of the use of clear toner as a specialty toner in this
invention.

[0030] The diverter 154 s a movable section of the paper path that can be
activated to either of the two positions. The diverter can be activated
by known means such as a solenoid, motor, compressed air, or vacuum. In
FIG. 4 it is shown that, in the duplex position, the receiver sheets are
directed toward the right underside (as shown by arrow R) and into the
reversing nip 152 (RN). Once the trail edge of the sheet clears the
diverter 154, the reversing rollers (154 (RR) reverse direction and move
the sheet towards the return path. The top of the diverter profile is
shaped to enable the trail edge of the sheet (which has now has become
the lead edge) to be picked up and guided over the top of the diverter
and towards the return path (180) for imaging the second side of the
sheet 111. When the diverter 154 is in the multi-pass simplex position
the lead edge is guided towards the left underside of the diverter into
the return path and back to transfer nip 2 119 for transfer of another
image or images to the same side of the sheet.

[0031] It should be noted that in the embodiment where development
stations 113A and 113B are not both used during a single pass of a
receiver sheet through the EP engine, the development stations can be
used alternatively by diverting receiver from the inverter and printing a
second simplex image on the same receiver sheet when the receiver passes
through the multi-development station 114 a second time.

[0032] It should be noted that, although the dual module 112 is shown in
the position of being at the extreme right and, accordingly, the last
station to transfer an image onto the ITM 150, it can be placed between,
before, subsequent to any other station, depending on the intended use.
Moreover, between any two stations, auxiliary components such as
conditioning chargers, cleaners, or fusers or image tackers can also be
installed. It should also be noted that, although the present example
incorporates an ITM web, alternative configurations such as separate ITM
drums in each EP module or direct transfer to the receiver is also
included in the present invention. It should also be noted that, for this
invention to work, the toners contained in each development station must
have the same polarity of the charge, irrespective of the type of
development station used. It is preferred that the toners be negatively
charged. The development stations need not all be similar. For example,
stations 110A, 110B, and 110C may employ a rotating magnetic core whereas
development station 110D may have a fixed magnetic core and a rotating
shell and development stations 113A and 113B can use a single component
developer. In addition, the primary imaging members need not be
identical. For example, the primary imaging members can differ in
diameter from one module to another, thereby allowing cylindrical primary
imaging members with smaller diameters, for example, of 30 mm to be used
in those modules containing a single development station and primary
imaging members of larger diameters such as 60 mm to be used in the
modules containing two or more development stations. Some modules can
also contain primary imaging members in the form of a web, whereas others
may contain cylindrical primary imaging members.

[0033] In the present example, the EP engine is configured so that the
PIMs rotate in a counterclockwise direction. In this scenario, it is
preferred that the position of the development station 113A be between
5:00 and 7:00, preferably at 6:00 and development station 113B be located
between 2:00 and 4:00 with respect to the cylindrical primary imaging
member employed in this example.

[0034] So-called single component development stations, i.e. those that do
not use or contain magnetic carrier particles to charge or transport the
toner particles and are well known in the art, can also be used in the
practice of the present invention. However, single component development
stations do not function well if located in the 6:00 position with
respect to the primary imaging member. In practicing this invention, a
module with two or more development stations can use one or more single
component development stations in that module. If the electrophotographic
print module contains a cylindrical primary imaging member and two
development stations of which one is a monocomponent development station
and one is a two-component development station; the two-component
development station should be located between the 5:00 and 7:00 position
and the monocomponent development station located between the 8:00 and
12:00 position with respect to the primary imaging member and in
sufficiently close proximity to the primary imaging member so as to allow
an electrostatic latent image on the primary imaging member to be
converted into a visible image for a primary imaging member running in a
counterclockwise direction. If the electrophotographic print module
contains a cylindrical primary imaging member and two monocomponent
development stations of; each development station should be located
between the 8:00 and 12:00 position with respect to the primary imaging
member and in sufficiently close proximity to the primary imaging member
so as to allow an electrostatic latent image on the primary imaging
member to be converted into a visible image for a primary imaging member
running in a counterclockwise direction.

[0035] If the electrophotographic print module contains a cylindrical
primary imaging member and two development stations of which one is a
monocomponent development station and one is a two-component development
station; the two-component development station should be located between
the 5:00 and 7:00 position and the monocomponent development station
located between the 4:00 and 12:00 position with respect to the primary
imaging member and in sufficiently close proximity to the primary imaging
member so as to allow an electrostatic latent image on the primary
imaging member to be converted into a visible image for a primary imaging
member running in a clockwise direction. If the electrophotographic print
module contains a cylindrical primary imaging member and two
monocomponent development stations of each development station should be
located between the 4:00 and 12:00 position with respect to the primary
imaging member and in sufficiently close proximity to the primary imaging
member so as to allow an electrostatic latent image on the primary
imaging member to be converted into a visible image for a primary imaging
member running in a clockwise direction.

[0036] In another embodiment of the present invention, multiple EP modules
containing a plurality of development stations are contained in the EP
engine. An example showing two modules containing two development
stations is shown in FIG. 2. Additional such modules incorporating a
plurality of development stations can also be included up to and
including all EP modules within the EP engine containing a plurality of
development stations. It is preferred that the plurality consist of two
development stations, as additional stations can present difficulties in
allocating sufficient space within the restrictions of the EP engine. It
should also be noted that the modules containing multiple development
stations 114 need not be located adjacent to one another and can, in
fact, be located anywhere along the development path. Thus, module 124
containing a multi-development station 114 having a plurality of
development stations and module 110B, for example, can be interchanged as
long as the control unit 210 (see FIG. 7) for the print engine is
programmed to know which modules are single development station modules
and which have a plurality of modules. In addition, sufficient space must
be allocated for any multiple module station. Finally, the control unit
must be programmed to specify which development station is to be used for
a given application when using EP modules with multiple development
stations.

[0037] Specialty toners 158 as shown in FIG. 1 a, consists of the group of
toners that extend the printing capabilities of an electrophotographic
engine beyond that obtainable with the conventional cyan, magenta,
yellow, and black subtractive primary colored toners used to convert the
electrostatic latent images of the cyan, magenta, yellow, and black
separations into visible images. Accordingly, color gamut enhancing
toners such as green, red, blue, and violet colored toners are specialty
toners. Dry inks can be designed to enhance color gamut, apply specialty
inks such as magnetic inks used by banks for tracking checks, a.k.a.
MICR, clear inks use for purposes such as enhancing gloss, providing
abrasion resistance, etc., inks containing security features such as
so-called "traceless components", etc. These are also specialty toners.
Specialty toners also include normal-size clear toner particles, i.e.
those having median volume weighted diameters in the range of
approximately 5 μm to 8 μm, that are often used to cover exposed
portions of a receiver such as paper to enable an image on that receiver
to be uniformly glossed. Alternatively, large clear toner, i.e. that
having a median volume-weighted diameter of greater than approximately 20
μm, is often used to allow raised letter printing and are considered
specialty toners. Low density toners, i.e. toners having the color of one
of the subtractive primary colors of cyan, magenta, yellow, or black so
that a monolayer of that toner, defined as a layer of toner such that a
microscopic examination would reveal a layer of toner covering between
60% and 100% of a primary imaging member would have a transmission
density in the primarily absorbed light color, as measured using a device
such as an X-Rite Densitometer with Status A filters of between 0.1 and
0.4 are also considered specialty toners.

[0038] Print jobs having job specifications, such as those supplied by a
customer, can be inputted into the presently described
electrophotographic apparatus in many known manners including submitting
electronic files directly, scanning original prints, etc. The operator
can directly specify which specialty toners, if any, are to be used for a
given print job. Alternatively, the control system for the
electrophotographic engine can determine what specialty toners are
required for a job. For example, the control system can determine from
the electronic file that low density cyan and green are needed to
accurately portray a scene depicting the coronation of a king on a clear
day. Alternatively, the operator can manually input into the machine that
these colors are to be included in printing the job. The separations are
rendered using known techniques and appropriate color corrections, such
as undercolor removal, as are known in the art, are implemented.

[0039] If, for example, the electrophotographic engine contains four EP
modules, of which two contain a single development station and two
contain two development stations each, the cyan. magenta, yellow, and
black separations can be printed and transferred to the receiver. The
image may or may not be fused, depending on the specified operating
conditions. The receiver is then diverted so as to not enter the inverter
162, but rather be allowed to pass through the print engine a second
time. This is sometimes referred to as a multipass print. The returning
receiver is of toner fused but could be fused to allow more options. The
low density cyan and the green separations are then printed in the
respective EP modules and transferred to the receiver on the same side of
the receiver that received the first set of separations. The image is
fused and diverted to the inverter so that duplexing imaging can be
performed, if desired. This mode is obviously just one of the variations
that can be used in practicing this invention. As few as a single module
or as many as all the modules can contain multiple development stations
and be used in this manner to expand printing capabilities of the EP
engine.

[0040] It is anticipated that job specification errors can occur when
printing using a multi development station. In order to correct any
resulting errors, including errors in the execution of a job that
requires the use of a multi-development station in an EP module, an error
correcting method is required. In one embodiment the error correction
method is used when a job requires red and green toners both be used on
the print and these two toners are contained in the multi-development
stations of a single EP module. The EP engine cannot print with both
toners at the same time so the job must resolve the error using the error
correction method and the correction module in the controller. The error
correction module in this embodiment has two distinct methods of
resolving the error that can be used depending on the situation. The
green can be printed first and the receiver ran through again for the red
toner or vice versa. The correcting module automatically chooses based on
the image and using the multi-development station.

[0041] For example, if the job specification explicitly specifies one or
more colorants that need to be employed in the process of preparing the
job for printing, also called rendering, an evaluation of the job data
can be made prior to preparing to determine which colorants would be the
best suited to fulfill the job and in what order. Preparing the job
includes processing image data by providing raterized color separations
(RIP Data), subjecting the rip data to processing and possibly comparing
it to the data source. This could be done by evaluating spot colors that
are specifically called out in the job (MICR, NexPress dimensional clear,
e.g.) or through analysis which determines the gamut of colors that would
provide the most faithful reproduction of the job. In this case, the
evaluation might lead to the conclusion that processing the colors in
addition to cyan, magenta, yellow, and black (CMYK) would result in a
more accurate rendition than (CMYK) alone. For example, in jobs that
contain photographs of people, additional colorants such as a light
magenta and light cyan that are specially formulated for photographic
reproduction may be determined to be the best colorants for the most
faithful color rendition of the job as compared to its original intent.

[0042] An additional processing alternative would be either through
specification or job data analysis determine the lay down order of the
colorants which would lead to the either the most faithful color
rendition or a unique desired effect. For example, a white colorant might
want to be flood coated or laid down over the entire surface prior to any
other colorants to achieve a certain effect.

[0043] Prior to the initiation of the process, an evaluation is made of
the available colorants in the EP engine, and is compared to the
colorants that have been selected by any of the methods previously
described.

[0044] In the method where a mismatch between the job specification and
the colorant that are available result in operator intervention, error
messages are displayed and the sequence of instructions to the operator
to correct the error are provided. These may include manual modification
of the job specification to eliminate unavailable colorants, or the
installation and/or the removal of specific colorant stations from the EP
engine to satisfy the mismatch condition. Once the error condition has
been satisfied, the job will be processed with planar data for all the
colorants required for the job.

[0045] In the method where there is an automated method of the EP Engine
self-correction, the job is processed and/or as above and the planar data
associated with colorants is supplied to the EP Engine when required. For
example, in a job that is determined to require seven colorants, in a
Tandem engine that can have only six colorants available for each pass
through the EP Process, the first six planes of data are sent to the EP
engine (i.e. cyan, magenta, yellow, black, light cyan, light magenta). On
the next pass through the EP engine, the next plane of data would be sent
to the EP engine such as the need for clear toner for glossing
applications.

[0046] The term planar data refers to color data that allows for the pixel
value organization that involves the separation of image data into two or
more planes, as is known and commonly used in the field of color science.

[0047] The EP printer can print by moving the receiver 111 past the print
modules one time or multiple times. An operator can also add instructions
via a control unit including touching apps on a screen in communication
with the controller. Alternatively the controller can refer to markings
or other indicators on parts of the printer, such as the development
station. If the receiver passes the modules one time it is commonly
referred to as a single pass. If it goes through multiple times it is a
multi pass print job. One embodiment of a multipass print job also
incorporates a control unit capable of self correcting a print or job
error. This method includes first printing by one or more of at least two
electrophotographic modules by first charging a primary imaging member,
creating an electrostatic latent image by image-wise exposing the one or
more primary imaging members; converting the electrostatic latent image
into a visible image by bringing the electrostatic latent image into
close proximity to a multi-development station in the one or more
electrophotographic modules; and transferring the visible image to an
intermediate transfer member. For a multi pass print then another pass is
made by the receiver after the receiver passes through the diverter
and/or inverter, to create at least one additional electrostatic latent
image by at least one of the electrophotographic modules. This image can
be made by a multi-development station or a single development station.
Then the electrostatic latent image is converted into a visible image by
bringing the electrostatic latent image into close proximity to this
development station in the electrophotographic module as the receiver
passes through a second time. The toned image is transferred to the
transfer intermediate member bearing the previously toned image on the
same side and/or the opposite side of the receiver as the previously
toned images and the toned image is transferred from the intermediate
transfer member to the receiver. Finally the toned image is made
permanent by fusing.

[0048] One of the challenges encountered when transferring a second image
to the sheet, especially for multi-pass simplex, is accurately aligning
the image to the sheet. Any registration errors can adversely affect this
alignment include: various in-track, skew, and cross-track positioning
errors occurring as the sheet moves thru the paper path from transfer nip
2 119 where the first image was transferred back to that transfer nip 2
119 for the second image transfer. Another error is due to shrinkage of
the sheet caused by removing moisture as the sheet passes thru the fuser.
It is necessary to control these errors using the control unit. For
example it is possible to apply countermeasures for correcting the
in-track, skew, and cross-track positioning errors and sheet shrinkage
for a given sheet or substrate type by adjusting various components and
their setups. The control used would access information such as in a look
up table (LUT) to do this.

[0049] In-track, skew, and cross-track positioning errors occur as the
sheet moves thru the paper path and also result from effects such as the
nip roller pairs 190 not being parallel to each other, nip force
unevenness front to rear, and roller coefficient of friction variations
front to rear or any roller pairs 192. These nip roller attributes are
part of the normal manufacturing tolerances that would be expected,
however they should remain fairly constant throughout the life of the
printer. These errors are, in one embodiment, measured using a pair of
sensors with one sensor 194 positioned close to the front of the receiver
sheet and one sensor 196 positioned close to the rear of the receiver
sheet for in-track position and skew. A third sensor array containing a
plurality of individual sensors 198 and positioned along either the front
or rear edge of the receiver, as shown in FIG. 7, would enable measuring
cross-track position by a method such as in FIG. 9. This sensor array can
measure variable cross-track widths.

[0050] This information would be recorded in a "look up" table 220 for
different sheet or substrate types (see top view sketch of sensors). This
information could then be used to predict the sheet to image error and
correction could take place using the image formation device. This device
such as an LED writer would adjust its placement of the image or images
on the photoconductor so that when it is transferred to the intermediate
web and then to the receiver sheet position at the second transfer nip is
correct. Sheet shrinkage could also be predicted and compensated for
using the same sensors and image formation device or devices. The printer
could also have a humidity and temperature sensors and these values could
be use to establish a calibration point at which the "look up" table was
established. Sheet or substrate shrinkage could be affected by the value
changes.

[0051] In one embodiment the error correction method includes the
following steps establishing a look up table of the actual position of
the receiver sheet edges; comparing the measured positions with the
reference positions in the look up table; determining a correction factor
from the difference between the reference positions and the measured
positions of the in-track front 232 and rear edges 234 and the cross
track edge; and adjusting the position of the electrostatic latent image
on the primary imaging member by varying the writer output. This method
can use an LED array for the writer.

[0052] The present invention offers yet another advantage over the
existing art. In other EP engines, receiver sheets exit the EP engine
most often face down because it is more consistent with the receiver
path. However, it is advantageous, in some instances such as when
generating color proofs, to allow the receiver to exit with the imaged
side up. A modification of the present invention allows the operator to
select the orientation of the exiting receiver sheet using controller
210. Specifically, as shown in FIG. 5, the addition of a second diverter
164, used in conjunction with the inverter diverter 154 which is part of
the inverter 162, enables the receiver to exit the EP engine face up. To
exit face up, the inverter diverter 154 is set allow the receiver sheet
to enter the inverter 162. A second inverter then is set to prevent the
receiver from reentering the paper path 180 in the loop that would result
in toned images being transferred to it, and, instead, directs the
receiver sheet to the exit in the face up configuration. While the face
up exit configuration would be normally used in simplex imaging, it can
also be used, if desired, in duplex imaging. In this instance, the toned
images are first transferred to the simplex side of the receiver. The
inverter diverter is first set to invert the sheet and the exit diverter
164 is set to allow the receiver to reenter the paper path 180 so that
images can be transferred to the duplex side. Upon completion of duplex
imaging, the sheet is again allowed to reenter the inverter, instead of
simply exiting the EP machine, and inverted. The exiting inverter is now
set to allow the duplexed print to exit the machine with the simplex side
face up.

[0053] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within the
spirit and scope of the invention.